NEWARK — A police officer who served as a Spanish interpreter for the mother of a juvenile arrested in the Newark schoolyard killings said the woman understood his Miranda instructions before allowing her 16-year-old son to give a statement.

The officer, Felipe Cantu, testified today in Superior Court in Newark at the murder trial of Alexander Alfaro, now 20, who is charged in the Aug. 4, 2007 crime. Five other young men were also charged in the shooting that left three college-bound friends dead and one injured.

Last year, a state appeals court ruled it would permit the statement Alfaro made to Virginia police on Aug. 18, 2007, in which he reportedly admitted cutting one of the victims with a machete. His attorney argued that Alfaro’s mother, Gloria Gomez, was not told she had a right to a lawyer before letting her son speak.

On the witness stand, Cantu, a police officer in Prince William County, Va., read from part of the written transcript. "He has to declare the pure truth," Gomez said, referring to her son. "I don’t want lies. Nothing."

Alfaro, who grew up in Newark and speaks English, did not need a translator. After he was arrested, Alfaro asked a detective, "‘Are you going to give me a chance to tell my side of the story?’" authorities have said.